Process of manufacturing filaments for incandescent electric lamps.



IINTED STATES PATENT OFFICE- FRITZ BAUMANN, OF AUGSBURG, GERMANY, ASSIGNOR TO THE FIRM OF WOLFRAM- LAMPEN AKTIENGESELLSCHAFT, OF AUGSBURG, GERMANY.

PROCESS OF MANUFACTURING llIIZHQIVIIELVJIS'IEEOR INCANDESCENT ELECTRIC LAMPS.

. Be it lmown that I, Dr. Fnrrz BAUIrLANN, a citizen of the German Empire, residing at Augsburg, Bavaria, Germany, have invented certain newand useful Improvements in Processes of Manufacturing Filaments for Incandescent Electric Lamps, of Which-the following is a specification.

My invention relates, to a process of manufacturing filaments consisting of tungsten containing small admixtures of metals, suchas chromium, vanadium, niobium, tantalum, osmium, ruthenium, zirconium and thorium, for electric incandescent lamps;

Filaments for electric incandescent lamps are well-known which consist of a sintered mixture of metallic tungsten containing small admixtures of metals, such as those mentioned above, which effect the sintering.- These filaments are made by finely divided metallic tungsten containingsmall admixtures of metals or oxids, which cause the sintering of the tungsten or other compounds of these metals, being formed into filaments in known manner after being mixed with a moldable organic binder, whereupon after carbonization the carbon is removed from the filaments likewise in known manner by heating them in an atmosphere of water vapor and hydrogen, whereupon the filaments are exposed for a few seconds to a very high temperature and thereby sintered. Incandescent filaments of great. strength and considerable elasticity have been obtained inthis manner.

rectly adding the additional metals or compounds and by correspondingly increased sintering, filaments are obtained which are not only-sufiiciently strong and very elastic, v but are immediately ductile and can be bent;

considerably without rupturing at ordinary temperatures; in other words, these incandescent filaments possess all the properties of a drawn wire. Such ductile incandescent bodies can be obtained by the usual pressing or paste process in-sizes such that the same can be used at once in the incandescent lamp manufacture of filaments by the paste process, however, is found in practice to be very troublesome and expensive Tbesides having many difficulties attached to A primary object of my invention isto provide a process consisting in makmg tung- S'pecification of Letters Patent.

, Careful tests have, however, shown that by cor-v Patented Nov. 14, 1916.-

Application filed Merch'S, 1913. Serial No. 753,135.

sten bodies of large dimensions or section containing an admixture of the said metals or metalllc' compounds, which cause the tungsten to sinter, and in heating said bodies to such a high temperature by the electric current that they are immedlately ductile and can be subjected to a drawing process. To this end I very intimately mix powdered metallic tungsten, or an oxid of tungsten,.

or "tungstic acid from which the metal is obtalned for example by reduction by means of hydrogen, with one or more of the said auxiliary metals, or with a suitable compound of these metals, or with several therei of, the proportions of the mixture dependingrentirel'y on the kind of the metal, or metals, or metallic compounds, and prelierably being between 0.1 and 10%. The quantity of the addition, if of metal, will be smaller, than if a compound of ametal is used. It must, in any event, be .in such quantity that a substantial amount of the added metal remains in the finished rod 01 bar. I then press these mixtures in well.- known. manner into rods or bars, using suitable molds and employing a very high pressure. The molding may be elfected with or without the aid of a binder, and the rods or bars may have a round, square or rectangue lar section. I then heat the metallic bodies thus molded in a reducing atmosphere, e. 9., hydrogen, or in oacuo for a considerable time toa temperature between1000 and 15009 C., when the same noticeably shrink and become/more solid. These preliminarily burnt rods or bars are then secured b suitable clamps in metallic receivers throug which hydrogen flows, and then alternat ing current of such a strength is passed through them that they are heated to almost of melting point. The strength of the current and the time during which it fiows' is dependent, on the one hand, on the se lected dimensions of the rod and, on thef other hand, on the kind and quantity of the 1'00 admixed metals Ora compounds.

As admixtures metallic thorium and compounds ofthorium have proved most suitable, and when the conditions are properly selected metallic bodies can be obtained. 105

having a square section of from 0.5 'to 8 mm; length of sidefwhich are directly flexible at ordinary temperatures after the sintering process is completed, and are not decidedly brittle and fragile like those of.,11o-

1 great brilliance,

pure metallic tungsten. The final product obtained after heating to such a high temperature must be considered to be an alloy or a solid solution of tungsten and the mentioned metal, thus, 6. 9., when thorium is changed. The mere appearance of these metallic bodies proves this. In contradistinction to rods of pure tungsten which are sintered in a similar manner and have a decided crystalline structure and a rather rough-surface, these metallic bodies have no traceof granulation or crystallization and have an absolutely smooth surface of very It is particularly important to employ a suitable starting material, to which the said metals or 'metallic com-. pounds areto be added in a state of fine distribution. A number of tests have shown that the *sintering process takes place most readily when amorphous tungsten is employed as starting material. The sintering can however be effected until ductilityis obtained also with all gradations of fineness of the metal from fine'to coarse crystalline.

It is, however, clear that the sintering process is then rather more diflicult and slower when it is wished to attain the same end. These rods which are already ductile can be directly subjected to the drawing process when they have'relativel'y small dimensions. If rods or bars oflarger dimensions are employed, however, for increasing capacity or for other reasons, it is necessary to reduce them previously to smaller dimensions. This can be simply done in well-known manner by rolling or hammering, and the take place at ordinary temperatures, or it may be performed more rapldly than at ordinary temperatures .when an increased temperature is employed.

Thus whereas in the otherwise customary process of manufacturing ductile wire of pure metallic tungsten, the same mustbe so changed in its physical and molecular properties after the sintering by repeated mechanical mering and the like, increased temperatures being constantly employed, that it gradually .becomes 'ductile even at'ordinary temperatures, according to the present process by means of large dimensions in the p shown lamps,

treatment, such as rolling, hamthe suitably conducted.- sintering process I obtain ductile metallic bodies which contain a high percentage of tungsten and can be readily drawn into the finest wires, This denotes considerable progress in the art and material simplification and reduction of cost of the process.

The real drawing process may be carried out from the beginning without employing high temperatures,but, of course, particularly at first, the process is facilitated by simultaneously using increased temperatures. The drawn wires are exceedinglystrong and their tensile strength is greater than that of pure tungsten wire. The result, 71. e.,the possibility of making ductile metallic bodies con taining such a high percentage of tungsten in the described manner, was the-more surprising owing -to numerous tests having that, when these bodies are used as filaments for electric incandescent lamps, in contradistinction to drawn pure tungsten wire they do not sufi'er any molecular changes and do not become brittle, like the latter, after long heating. Even after burning for athousand and more hours the new wires can'be bent at ordinary temperatures without breaking. Whereas drawn wire composedof pure tungsten hasthe great disadvantage that its structure changes completely after it has burnt for a relatively short time, as it again assumes the structure of the starting material and thereby becomes brittle and fragile, in the ductile metallic bodies made according to my; improved processthis phenomenon is not met with, this being an additional proof that me-' tallic tungsten has experienced during the sintering process, and owing to the admixtures, a thorough physical change owing to the formation of tion which no longer allows the tungsten to recover .its original non-ductile condition. At first it was feared that when these wires were heated for a long time in incandescent ually'distilled out and that the lamp bulbs would 'be blackened and the light dimin ished. A series of electric, photometric and chemical investigations has, however, shown that this is not the case, but that the. admix- 1 t-ures quantitatively remainv in the wire. On the contrary, it has been found that these wires offer greater resistance to atomization than pure tungsten wlreand consequently can be more severely loaded, so that lamps 1 can be made with them possessinga specific consumption of energy less than 1.0 watts per Hefner candle-power.

I claim 1. The process of manufacturing a duc- 1 tile rod or bar containing a large percentage of metallic tungsten and alloyed therewith a small admixture .of an auxiliary, preferably highly refractory metal, which consists in intimately mixing finely-divided tungsten 1 an alloy or a solid solu- 10 the auxiliary metals would be grad- 1:

or a compound thereof with a small proportion, from 0.1 per cent. to ten per cent., of such finely-divided auxiliary metal or a compound thereof, in pressing the mixture thus obtained into the form of a bar, then heating the bar in a non-oxidizing atmosphere for a considerable time to a temperature between 1000 and 15,00 0. to shrink and solidify the bar, and then heating the bar now consisting of tungsten alloyed with the auxiliary metal almost to the melting point in a reducing atmosphere, whereby the bar is sintered and on cooling can be stretched, rolled or drawn.

2. The process of manufacturing a duotile rod or bar containing a large percentage of-m etallic tungsten and a small admixture of metallic thorium, which consists in intimately mixing finely-divided tungsten or a compound thereof With a small proportion, from 0.1 per cent. to ten per cent., of thorium or a compound thereof, in pressing the mixture thus obtained into the form of a bar, then heating the bar in a nonoxidizing atmosphere for a considerable time to a temperature between 1000 and 1500 C. to shrink and solidify the bar, and then heating the bar now consisting of tungsten alloyed with thorium almost to the .ture between 1000 and 1500 C. to shrink and solidify the bar, and then heating the bar almost to the melting point in a reducing atmosphere, whereby the bar is sintered and on cooling can be stretched, rolled or drawn.

In testimony whereof I afiix my signature in presence of two witnesses.

DR. FRITZ BAUMA NN.

lVitnesses:

RICHARD LEMP, JOHANNA STERN. 

